Research suggests that different types of sedentary behavior may affect dementia risk in different ways, a finding that could help shape future prevention strategies.
What if the biggest threat to brain health is not how long we sit, but what we do while sitting? New research suggests that mentally passive activities, such as prolonged TV watching, may raise the risk of dementia, while more mentally engaging sedentary behaviors could help protect the brain as people age.
The findings, published in the American Journal of Preventive Medicine by Elsevier, challenge the long-held idea that all sitting is equally harmful. Researchers say the study could help reshape public health recommendations by showing that keeping the brain active during sedentary time may play a key role in lowering dementia risk later in life.
Dementia prevention needs sharper targets
Populations around the world are aging. Dementia is the third leading cause of death and the seventh leading cause of disability among older adults globally. It is a common age-related condition that affects quality of life for many adults, as well as their families and caregivers. Prevention matters, and one important step is identifying risk factors that people may be able to change.
For years, sedentary behavior was generally viewed as a dementia risk. More recent research, however, suggests that the picture is more specific. Mentally passive sedentary behaviors (such as watching TV) have been linked to a higher risk of depression, while mentally active sedentary behaviors (such as reading and office work) seem to offer protection.
Most adults sit for about 9 to 10 hours each day. Earlier studies have linked long, uninterrupted sitting with cardiovascular disease, type 2 diabetes, and depression. Sitting has also been associated with dementia.
This is the first study to separate mentally passive sitting from mentally active sitting when examining dementia risk.
Brain activity may matter
Lead investigator Mats Hallgren, PhD, Department of Public Health Sciences, Karolinska Institute, Sweden, and Baker Deakin Department of Lifestyle and Diabetes, Institute for Physical Activity and Nutrition (IPAN), Deakin University, Australia, notes, “While all sitting involves minimal energy expenditure, it may be differentiated by the level of brain activity. How we use our brains while we are sitting appears to be a crucial determinant of future cognitive functioning and, as we have shown, may predict dementia onset.”
Researchers studied data from a long-term project that followed 20,811 adults ages 35 to 64 for 19 years (1997-2016). The initial survey asked about sedentary behaviors, physical activity, and other behaviors linked to dementia. New dementia cases were identified by connecting the 1997 survey data with the Swedish National Patient Register and the Swedish Cause of Death Register.
Using several statistical models, investigators evaluated how dementia risk changed when mentally passive sedentary behaviors were (statistically) replaced with mentally active sedentary behaviors. “The prospective study design allowed us to establish the direction of these relationships and infers but does not establish causality. Controlled trials are needed to confirm these important observational study findings,” notes Dr. Hallgren.
The study’s main findings are as follows:
- Mentally active sedentary behavior was linked to a lower risk of developing dementia among adults in middle age and older adulthood.
- Spending more time in mentally active sedentary behavior was associated with a significant reduction in dementia risk, even when levels of passive sedentary behavior, light physical activity, and moderate to vigorous physical activity were maintained.
- Replacing time spent in mentally passive sedentary behavior with the same amount of mentally active sedentary behavior was also associated with a lower risk of developing dementia.
Prevention may need sharper advice
Because the data were collected through an extensive survey covering (3,600 cities and villages across Sweden), the investigators believe the results are likely relevant to a broader global population.
Dr. Hallgren concludes, “Sedentary behavior is a ubiquitous but modifiable risk factor for many health conditions, including dementia. Our study adds the observation that not all sedentary behaviors are equivalent; some may increase the risk of dementia, while others may be protective. It is important to remain physically active as we age, but also mentally active—especially when we are sitting.”
Reference: “Mentally Active Versus Passive Sedentary Behavior and Risk of Dementia: 19-Year Cohort Study” by André O. Werneck, Michael J. Wheeler, David W. Dunstan, Neville Owen, Ylva Trolle Lagerros and Mats Hallgren, 25 March 2026, American Journal of Preventive Medicine.
DOI: 10.1016/j.amepre.2026.108317
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